The OEIS is supported by the many generous donors to the OEIS Foundation.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #26 Nov 03 2024 02:03:55
%S 7,13,19,5,31,37,43,7,5,61,67,73,79,5,7,97,103,109,5,11,127,7,139,5,
%T 151,157,163,13,5,181,11,193,199,5,211,7,223,229,5,241,13,11,7,5,271,
%U 277,283,17,5,7,307,313,11,5,331,337,7,349,5,19,367,373,379,5,17,397,13,409
%N Smallest prime factor of 6*n+1.
%C If 6*n+1 is prime, a(n) = 6*n+1.
%H Amiram Eldar, <a href="/A107744/b107744.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A020639(A016921(n)). - _Amiram Eldar_, Nov 03 2024
%t A107744[n_]:= FactorInteger[6 n + 1][[1, 1]]
%o (PARI) vector(100, n, vecmin(factor(6*n+1)[, 1])) \\ _Altug Alkan_, Oct 23 2015
%o (Magma) [Min(PrimeFactors(6*n+1)):n in[1..68]]; // _Jason Kimberley_, Oct 28 2015
%Y Cf. A016921, A020639.
%Y Cf. A107745 (smallest prime factor of 6*n-1), A107746 (values of k such that A107744(k) > A107745(k)), A107747 (values of k such that A107744(k) < A107745(k)).
%K nonn
%O 1,1
%A _Zak Seidov_, May 23 2005
%E Comments corrected and (at the suggestion of _Michel Marcus_) moved to Crossrefs by _Jason Kimberley_, Oct 23 2015